According to 3GPP TS 36.331, which is herein incorporated by reference in its entirety, there are two main types of measurements made by the UE (user equipment) in E-UTRAN (Evolved Universal Terrestrial Radio Access Network)—periodic and event-based. All measurements are configured by the eNodeB, but are performed by the UE. The measurements are sent in one or several RRCConnectionReconfiguration messages.
Periodic measurements are configured per frequency layer and imply that the UE sends periodical measurement reports. A frequency layer is a frequency or a group of frequencies of a specific RAT (radio access technology). Event-based measurements use the same UE measurements as the periodic measurements, but the UE will only report when an event criterion is fulfilled. The event criterion can for example be of type “Serving becomes better than absolute threshold”.
The eNodeB can order several measurements on same or different frequency layers. The measurements can be ordered on a need basis, i.e., not all measurements need be ordered in one RRCConnectionReconfiguration message. The UE-EUTRA-Capability IE (Information Element) indicates which frequency bands and RATs the UEs are capable of measuring.
A UE measurement typically consists of a MeasurementObject IE and a ReportConfig IE connected together by a MeasID IE. The MeasurementObject IE represents a frequency layer, i.e., a frequency or a frequency group of a specific RAT. The ReportConfig IE indicates the type of measurement, periodic or event-based, the quantity to measure on, etc.
The UE measurements can be used for different purposes, such as for mobility, SON (self organizing network), PM (performance management) and positioning. Operators may have one or more legacy RANs (radio access networks) where some may be of higher priority than others. For example, it is expected that the operator prefers to have the UEs connected to the RAN that provides highest throughput. For UEs that only have one receiver, measurements on different frequency layers must be performed in sequence.
Currently, the eNodeB has no control in which order the UE will perform the different measurements that are configured in the UE. If there are ongoing measurements in the UE and the eNodeB initiates new measurements, the eNodeB cannot control whether the new measurements shall interrupt the ongoing measurements or not.